Radiation image detection apparatus and manufacturing method of radiation image detector

ABSTRACT

In a radiation image detection apparatus having a radiation image detector that includes the following stacked in the order listed below: a bias electrode, a photoconductive layer, a substrate side charge transport layer, and an active matrix substrate, the radiation image detector does not include an area adjacent to the interface between the substrate side charge transport layer and photoconductive layer having an oxygen or chlorine element density not less than two times the average density of oxygen or chlorine element in the substrate side charge transport layer.

This application is a divisional application of U.S. application Ser.No. 12/343,995, filed Dec. 24, 2008, which claims priority to JP2007-340007, filed Dec. 28, 2007, each of which is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation image detection apparatushaving a radiation image detector that generates electric charges byreceiving a recording electromagnetic wave representing a radiationimage and records the radiation image by storing the electric charges.The invention also relates to a manufacturing method of the radiationimage detector.

2. Description of the Related Art

Various types of radiation image detectors that record a radiation imageof a subject by receiving radiation transmitted through the subject havebeen proposed and put into practical use in medical and other fields.

For example, radiation image detectors using amorphous selenium thatgenerates electric charges by receiving radiation are known, and aso-called TFT readout type is proposed as one of such radiation imagedetectors.

As for the TFT readout type radiation image detectors, for example, thefollowing detector is proposed. That is, a detector that includes thefollowing stacked on top of another: a bias electrode to which a biasvoltage is applied; a photoconductive layer that generates electriccharges by receiving radiation; and an active matrix substrate havingmultiple pixels disposed two-dimensionally, each with a chargecollecting electrode for collecting the electric charges generated inthe photoconductive layer, a storage capacitor for storing the electriccharges collected by the charge collecting electrode, and a TFT switchfor reading out the electric charges stored in the storage capacitor.

When recording a radiation image in the TFT readout type radiation imagedetector, radiation transmitted through a subject and representing aradiation image of the subject is irradiated on the radiation imagedetector from the bias electrode side, while, for example, a positivevoltage is applied to the bias electrode from a power source.

The radiation irradiated on the radiation image detector transmitsthrough the bias electrode, and is irradiated on the photoconductivelayer. Then, electric charge pairs are generated in the photoconductivelayer by the irradiation of the radiation, and the negative charges ofthe electric charge pairs are combined with positive charges charged onthe bias electrode and dissolved, while the positive charges of thecharge pairs are collected by each charge collecting electrode of eachpixel of the active matrix substrate and stored in each storagecapacitor as latent image charges, whereby the radiation image isrecorded.

Thereafter, the electric charges stored in the storage capacitors areread out by turning ON the TFT switches on the active matrix substrateaccording to control signals outputted from a gate driver and the chargesignals are detected by charge amplifiers, whereby image signalsaccording to the radiation image are read out.

As one of the radiation image detectors using the active matrixsubstrate described above, for example, U.S. Pat. No. 6,642,534 proposesa radiation image detector that includes a bias electrode, a Se-basedX-ray detection layer, a charge transport layer formed of Sb₂S₃, and anactive matrix substrate stacked on top of another. The aforementionedpatent publication describes that the provision of the charge transportlayer may prevent injection of electron holes into the X-ray detectionlayer from the active matrix substrate, whereby image qualitydegradation is prevented.

In a radiation image detector having the charge transport layer, theinterface between the charge transport layer and X-ray detection layerbecomes the interface through which the electric charges generated inthe X-ray detection layer by the irradiation of X-rays are transported.A study conducted by the inventor of the present invention, however, hasrevealed that impurities, such as oxygen, water, chloride compound, andthe like, may sometimes deposit in the interface depending on themanufacturing method, whereby electric charges generated in the X-raydetection layer are trapped. The study has also revealed that the trapeffect may give a favorable or unfavorable influence to the imagequality depending on the position of the charge transport layer in thedetector.

In view of the circumstances described above, it is an object of thepresent invention to provide a radiation image detection apparatushaving a high image quality radiation image detector capable ofappropriately controlling the charge traps described above. It is afurther object of the present invention to provide a manufacturingmethod of the radiation image detector.

SUMMARY OF THE INVENTION

A radiation image detection apparatus of the present invention is anapparatus having a radiation image detector that includes the followingstacked in the order listed below:

a bias electrode to which a bias voltage is applied;

a photoconductive layer that generates electric charges by receiving arecording electromagnetic wave representing a radiation image;

a substrate side charge transport layer that transports the electriccharges generated in the photoconductive layer; and

an active matrix substrate having multiple charge collecting electrodesdisposed thereon for collecting the electric charges generated in thephotoconductive layer,

wherein the radiation image detector does not include an area adjacentto the interface between the substrate side charge transport layer andphotoconductive layer having an oxygen or chlorine element density notless than two times the average density thereof in the substrate sidecharge transport layer.

The radiation image detection apparatus described above may furtherincludes a bias electrode side charge transport layer between the biaselectrode and photoconductive layer, and the bias electrode side chargetransport layer may include an area having an oxygen element density notless than three times the average density thereof in the bias electrodeside charge transport layer.

Further, the bias electrode side charge transport layer may be a layerthat includes antimony sulfide.

Still further, the bias electrode side charge transport layer may havean average composition of Sb_(x)S_(100-x) (41≦x≦60).

Further, the apparatus may further include an organic polymer layer thatincludes an electron hole blocking material between the bias electrodeside charge transport layer and photoconductive layer.

Still further, the electron hole blocking material may be at least onetype of carbon cluster selected from a group consisting of FullereneC₆₀, Fullerene C₇₀, fullerene oxide, and derivatives thereof.

Further, the apparatus may further include a light emitting means foremitting light on the radiation image detector from the side of theactive matrix substrate while at least the recording electromagneticwave is irradiated on the radiation image detector, and the substrateside charge transport layer may have a transmission factor not greaterthan 10% for the light.

Still further, the substrate side charge transport layer may be a layerthat includes antimony sulfide.

Further, the substrate side charge transport layer may have an averagecomposition of Sb_(x)S_(100-x) (41≦x≦60).

A first radiation image detector manufacturing method of the presentinvention is a manufacturing method of a radiation image detector thatincludes the following stacked in the order listed below: a biaselectrode to which a bias voltage is applied; a photoconductive layerthat generates electric charges by receiving a recording electromagneticwave representing a radiation image; a substrate side charge transportlayer that transports the electric charges generated in thephotoconductive layer; and an active matrix substrate having multiplecharge collecting electrodes disposed thereon for collecting theelectric charges generated in the photoconductive layer, the methodincluding the steps of:

forming the substrate side charge transport layer on the active matrixsubstrate in a vacuum chamber; and

without exposing the substrate side charge transport layer to gas thatincludes oxygen or water, forming thereon the photoconductive layer.

A second radiation image detector manufacturing method of the presentinvention is a manufacturing method of a radiation image detector thatincludes the following stacked in the order listed below: a biaselectrode to which a bias voltage is applied; a photoconductive layerthat generates electric charges by receiving a recording electromagneticwave representing a radiation image; a substrate side charge transportlayer that transports the electric charges generated in thephotoconductive layer; and an active matrix substrate having multiplecharge collecting electrodes disposed thereon for collecting theelectric charges generated in the photoconductive layer, the methodincluding the steps of:

forming the substrate side charge transport layer on the active matrixsubstrate in a vacuum chamber;

exposing the substrate side charge transport layer to gas that includesoxygen or water and returning the layer to the vacuum chamber; and

exposing the substrate side charge transport layer to an environmentaltemperature not less than 100° C. and forming thereon thephotoconductive layer.

In the first or second radiation image detector manufacturing method,the radiation image detector may further includes a bias electrode sidecharge transport layer between the bias electrode and photoconductivelayer, and the method may further include, following the step of formingthe photoconductive layer, the steps of exposing the photoconductivelayer to gas that includes not less than 1 vol % of oxygen or water, andreturning the photoconductive layer to the vacuum chamber and formingthereon the bias electrode side charge transport layer.

According to the radiation image detection apparatus of the presentinvention, the radiation image detector does not include an areaadjacent to the interface between the substrate side charge transportlayer and photoconductive layer having an oxygen or chlorine elementdensity not less than two times the average density thereof in thesubstrate side charge transport layer. This allows the reduction ofcharge trap density due to impurities, such as oxygen, chlorine, and thelike, whereby image lag characteristics may be improved.

Further, where the radiation image detection apparatus further includesa bias electrode side charge transport layer between the bias electrodeand photoconductive layer, and the bias electrode side charge transportlayer includes an area having an oxygen element density not less thanthree times the average density thereof in the bias electrode sidecharge transport layer, the area functions as a charge blocking layerthat reduces the amount of electric charges drawn into thephotoconductive layer from the bias electrode while the recordingelectromagnetic wave is irradiated. As the result, short term lag, to bedescribed later, may be reduced.

Still further, where the bias electrode side charge transport layer hasan average composition of Sb_(x)S_(100-x) (41≦x≦60), the compositionratio of Sb in the bias electrode side charge transport layer may becomegreater than the stoichiometric composition, whereby electrontransportability may be improved. This allows electric charges trappedin the bulk of the photoconductive layer to be discharged to the biaselectrode more efficiently, whereby long term lag characteristics, to bedescribed later, may be improved.

Further, where an organic polymer layer that includes an electron holeblocking material is further provided between the bias electrode sidecharge transport layer and photoconductive layer, defects in theinterface of the photoconductive layer on the side of the bias electrodemay be reduced. This may reduce electric charges trapped in the defectsand improve short term lag characteristics, to be described later.

Still further, where a light emitting means for emitting light on theradiation image detector from the side of the active matrix substratewhile at least the recording electromagnetic wave is irradiated on theradiation image detector is further provided, and the substrate sidecharge transport layer has a transmission factor not greater than 10%for the light, the light emitted from the light emitting means may beprevented from reaching the inside of the photoconductive layer of theradiation image detector, whereby dark current generated by the emissionof the light may be prevented.

Further, where the substrate side charge transport layer has an averagecomposition of Sb_(x)S_(100-x) (41≦x≦60), the composition ratio of Sb inthe substrate side charge transport layer may become greater than thestoichiometric composition, whereby the light may be preventedsufficiently from reaching the inside of the photoconductive layer.

According to the first radiation image detector manufacturing method ofthe present invention, the substrate side charge transport layer isformed on the active matrix substrate in a vacuum chamber, and withoutexposing the substrate side charge transport layer to gas that includesoxygen or water, the photoconductive layer is formed thereon. Thisallows the radiation image detector to be manufactured withoutdepositing impurities that trap electric charges in the interfacebetween the substrate side charge transport layer and photoconductivelayer.

According to the second radiation image detector manufacturing method ofthe present invention, the substrate side charge transport layer isformed on the active matrix substrate in a vacuum chamber, then thesubstrate side charge transport layer is exposed to gas that includesoxygen or water and returned to the vacuum chamber, and after exposingthe substrate side charge transport layer to an environmentaltemperature not less than 100° C., the photoconductive layer is formed.That is, even though the substrate side charge transport layer isexposed to gas that includes oxygen or water, the method may providecomparative effects to those of the first radiation image detectormanufacturing method by performing a baking process on the substrateside charge transport layer.

Further, in the first or second radiation image detector manufacturingmethod, where the radiation image detector further includes a biaselectrode side charge transport layer between the bias electrode andphotoconductive layer, and the manufacturing method further includes,following the step of forming the photoconductive layer, the steps ofexposing the photoconductive layer to gas that includes not less than 1vol % of oxygen or water, and returning the photoconductive layer to thevacuum chamber and forming the bias electrode side charge transportlayer, an area that includes more oxygen element and capable of actingas a charge blocking layer may be formed in the bias electrode sidecharge transport layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of the radiation imagedetection apparatus according to the present invention.

FIG. 2 a plan view of an active matrix substrate of the radiation imagedetector shown in FIG. 1.

FIG. 3 illustrates the composition of a second charge transport layerand a photoconductive layer when formed consecutively.

FIG. 4 illustrates the composition of the second charge transport layerand photoconductive layer when not formed consecutively.

FIG. 5 illustrates the composition of a first charge transport layer andthe photoconductive layer when not formed consecutively.

FIG. 6 illustrates the composition of the first charge transport layerand photoconductive layer when formed consecutively.

FIG. 7 illustrates evaluation results of dark current, short term lag,and long term lag of example radiation image detectors of the radiationimage detection apparatus of the present invention and a comparativeexample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an exemplary embodiment of the radiation image detectionapparatus according to the present invention will be described withreference to the accompanying drawings. The radiation image detectionapparatus of the present embodiment includes a so-called TFT readouttype radiation image detector. FIG. 1 is a cross-sectional view of theradiation image detection apparatus of the present embodiment,illustrating a schematic configuration thereof.

The radiation image detection apparatus of the present embodimentincludes radiation image detector 10 that generates electric charges byreceiving radiation and records a radiation image by storing the chargestherein, and surface light source 20 that emits light on radiation imagedetector 10 while radiation is irradiated thereon.

Radiation image detector 10 includes the following stacked in the orderlisted below: bias electrode 1 to which a bias voltage is applied, firstcharge transport layer 2 (bias electrode side charge transport layer ofthe present invention), organic polymer layer 3, photoconductive layer 4that generates electric charges by receiving radiation representing aradiation image, second charge transport layer 5 (substrate side chargetransport layer of the present invention) that transports the electriccharges generated in photoconductive layer 4, and an active matrixsubstrate 6 having multiple charge collecting electrodes disposedthereon for collecting the electric charges generated in thephotoconductive layer and transmitted through second charge transportlayer 5.

Bias electrode 1 is formed of a conductive material having a lowresistance, such as Au, Al, or the like. It is noted that a positivebias voltage is applied to bias electrode 1 of the radiation imagedetector of the present embodiment.

First charge transport layer 2 is formed of a material that includesantimony sulfide. The average composition of the antimony sulfide isSb_(y)S_(100-y) (41≦y≦60). More preferably, the value of y is 42≦y≦50.Further, first charge transport layer 2 includes an area having anoxygen element density not less than three times the average densitythereof in first charge transport layer 2. For example, the area may beformed in first charge transport layer 2 adjacent to the interfacethereof on the side of photoconductive layer 4. A method for forming thearea will be described later. The term “adjacent to the interface” asused herein refers to the range, when the composition of first chargetransport layer 2 is measured from the side of first charge transportlayer 2 toward photoconductive layer 4, from a point where the densityof the major component of first charge transport layer 2 startsdecreasing from the average density thereof in first charge transportlayer 2 to a point where the density thereof is decreased to about 1/100of the average density. Although it is preferable that first chargetransport layer 2 be provided, but is not necessarily required.

Organic polymer layer 3 is formed of an organic polymer material with anelectron hole blocking material added thereto. As for the organicpolymer material, for example, polycarbonate may be used. As for theelectron hole blocking material, for example, at least one type ofcarbon cluster selected from the group consisting of Fullerene C₆₀,Fullerene C₇₀, fullerene oxide, and derivatives thereof may be used.Although it is preferable that organic polymer layer 3 be provided, butis not necessarily required.

Photoconductive layer 4 has electromagnetic conductivity and generateselectric charges therein when irradiated with radiation. As for thematerial of photoconductive layer 4, for example, a-Se, HgI₂, PbI₂, CdS,CdSe, CdTe, BiI₃, or the like may be used. In particular, anamorphous-based a-Se film with a film thickness in the range from 100 to1000 μm is preferably used.

Second charge transport layer 5 is formed of a material with the averagecomposition of Sb_(x)S_(100-x) (41≦x≦60). More preferably, the value ofx is 42≦x≦50. Further, preferably the thickness of second chargetransport layer 5 is not less than 0.5 μm, and more preferably about 2μm. Still further, it is preferable that second charge transport layer 5be formed so as to have a transmission factor in the range from 0.01 to10% for the light (with a wavelength about 525 nm in the presentembodiment) emitted from surface light source 20. For example, the valueof transmission factor described above may be obtained by adjusting thecomposition ratio of Sb or the thickness.

Further, in the radiation imaged detector of the present embodiment,photoconductive layer 4 and second charge transport layer 5 are formedsuch that an area having an oxygen or chlorine element density not lessthan two times the average density thereof in second charge transportlayer 5 is not formed adjacent to the interface between photoconductivelayer 4 and second charge transport layer 5. A method for formingphotoconductive layer 4 and second charge transport layer 5 in themanner as described above will be described later. The term “adjacent tothe interface” as used herein refers to the range, when the compositionof second charge transport layer 5 is measured from the side of secondcharge transport layer 5 toward photoconductive layer 4, from a pointwhere the density of the major component of second charge transportlayer 5 starts decreasing from the average density thereof in secondcharge transport layer 5 to a point where the density thereof isdecreased to about 1/100 of the average density.

Further, second charge transport layer 5 may be formed of at least oneof cerium oxide, zinc selenide, zinc telluride, zinc sulfide, andarsenic selenide, other than antimony sulfide. Where second chargetransport layer 5 is formed of cerium oxide, it is formed so as not toinclude an area with a chlorine element density not less than two timesthe average density thereof in second charge transport layer 5.

Now referring to FIG. 2, there is shown a plan view of active matrixsubstrate 6. As illustrated in detail in FIG. 2, active matrix substrate6 includes multiple pixels 60 disposed two-dimensionally, each havingcharge collecting electrode 61 for collecting electric charges generatedin photoconductive layer 4, storage capacitor 62 for storing theelectric charges collected by charge collecting electrode 61, and TFTswitch 63 for reading out the electric charges stored in storagecapacitor 62. In addition, multiple scanning wires 64 for turning ON/OFFTFT switches 63 of respective pixels 60 and multiple data wires 65 forreading out electric charges stored in storage capacitors 62 aredisposed in a lattice pattern. Readout circuit 70 that includes anamplifier for reading out signal charges flowing out to each data wire65 is connected at the end thereof, and each scanning wire 64 isconnected to a gate driver 80 that outputs a control signal for turningON/OFF each TFT switch 63.

As for the material of charge collecting electrode 61 of active matrixsubstrate 6, any material may be used as long as it is a conductivematerial, but the electrode is preferable to transmits visible lightand, for example, ITO or IZO may preferably be used for that purpose.

Surface light source 20 is a light source of surface mountedlight-emitting diodes with a center emission wavelength of about 525 nm.Surface light source 20 may be provided separately from radiation imagedetector 10, as shown in FIG. 1, or it may be bonded to active matrixsubstrate 6 by an adhesive. Surface light source 20 is capable ofuniformly emitting light on photoconductive layer 4 by transmittingthrough active matrix substrate 6, while radiation is irradiated onradiation image detector 10. It is noted that active matrix substrate 6and the adhesive described above are transparent to the wavelength oflight emitted from surface light source 20.

Reasons for providing surface light source 20 as in the radiation imagedetection apparatus of the present invention will now be described.

In radiation image detector 10 that uses active matrix substrate 6,electrodes or the like for discharging electric charges are not providedat the spaces between charge collecting electrodes divided with respectto each pixel, so that electric charges generated by the irradiation ofradiation tend to accumulate in the spaces. As the result, the electricfield formed in photoconductive layer 4 by the application of a voltageto bias electrode 1 is distorted and the sensitive area ofphotoconductive layer 4 is varied, posing a problem of fluctuation ofthe sensitivity thereof. Another problem is that the charges accumulatedin the spaces between the charge collecting electrodes are graduallydischarged as image lag when reading out charge signals after theirradiation of radiation is stopped, whereby image lag characteristicsare degraded (in particular, it is problematic in short-term lag to bedescribed later).

Consequently, in the radiation image detector of the present embodiment,surface light source 20 is provided for emitting backlight from the sideof active matrix substrate 6. Emission of backlight to radiation imagedetector 10 by surface light source 20 while irradiating radiation onradiation detector 10 allows electric charges to be accumulated in thespaces between the charge collecting electrodes in advance, whereby theelectric field formed in photoconductive layer 4 may be distorted inadvance. Consequently, electric charges generated by the irradiation ofradiation move along the electric field distorted in advance withoutaccumulating in the spaces and are collected by the charge collectingelectrodes. That is, the variation in the sensitive area ofphotoconductive layer 4, and hence sensitivity variation, may beprevented. Further, continuation of the backlight emission after theradiation is stopped may prevent the electric charges accumulated in thespaces between charge collecting electrodes from gradually dischargingas image lag output.

Further, in the present embodiment, a so-called direct conversion typeradiation image detector that directly converts radiation to electriccharges has been described. But the present invention is not limited tothis, and may also be applied to a radiation image detector having aconfiguration similar to that of a so-called indirect conversion typeradiation image detector that converts radiation to light by a phosphorfirst, and then converts the light to electric charges. The term“radiation image detector having a configuration similar to that ofindirect conversion type radiation image detector” as used herein refersto a radiation image detector that includes a a-Se layer thinner thanthat of the direct conversion type radiation image detector, a lighttransmissive bias electrode, and a phosphor above the bias electrode,thereby converting light emitted from the phosphor to electric charges.In a radiation image detector configure in the manner as describedabove, the thickness of the photoconductive layer is about 1 to 30 μmand the storage capacitors are not essential.

Still further, in the radiation image detector of the presentembodiment, an active matrix substrate having multiple TFT switchesdisposed thereon is used. But the present invention may also be appliedto a radiation image detector that includes an active matrix substratehaving multiple switching elements, such as MOS switches, disposedthereon.

EXAMPLES

Examples of radiation image detector of the radiation image detectionapparatus of the present invention will now be described in detail.

Example 1

Example 1 of the radiation image detector will be described.

Example 1 of the radiation image detector was produced in the followingmanner. First, antimony sulfide material with composition of Sb₄₅S₅₅ isput in a crucible, then the crucible and active matrix substrate 6 areput in a deposition system, and the inside of the deposition system isvacuumed.

Then, the crucible holding the Sb₄₅S₅₅ is heated by a resistive heaterto heat the Sb₄₅S₅₅ to a temperature of 530° C., whereby second chargetransport layer 5 is formed on active matrix substrate 6 with a filmthickness of 2 μm.

Incidentally, the antimony sulfide material with composition of Sb₄₅S₅₅may be produced as follows. First, amounts of simple sulfur andantimony, each corresponding to each desired composition ratio, aremeasured and measured amounts are put in a glass vessel. Then the vesselis vacuumed and sealed, and while the glass vessel is heated to atemperature of the melting point of antimony (630° C.) or higher, theglass vessel is shaken and agitated (for 15 hours or more) to obtainantimony sulfide melt with uniform composition. Thereafter, the antimonysulfide melt is naturally cooled, whereby the antimony sulfide materialwith the desired composition may be produced.

Further, the composition of second charge transport layer may bemeasured by various methods including the following:

-   -   1) after exposing the measuring target layer, digging down the        layer by ion sputtering and measuring the composition by        secondary ion mass spectrometer (SIMS),    -   2) carving out a cross-section of the radiation image detector        and mapping the composition of the portion corresponding to        second charge transport layer 5 by energy dispersive X-ray        analyzer (EDX),    -   3) scratching off the portion corresponding to second charge        transport layer from the radiation image detector and measuring        the average composition thereof by X-ray fluorescence        spectrometry (XRF), and    -   4) separating the radiation image detector in the layer stacking        direction adjacent to second charge transport layer 5 and        performing the measurement by thin-film XRF.

Following the formation of second charge transport layer 5 on activematrix substrate 6 in the vacuum chamber in the manner as describedabove, Se material that includes 10 ppm of Na is deposited on secondcharge transport layer 5 to form photoconductive layer 4 of amorphous Sehaving a film thickness of 1000 μm without exposing second chargetransport layer 5 to gas that includes oxygen or water.

Formation of photoconductive layer 4 without exposing second chargetransport layer 5 to gas that includes oxygen or water in the manner asdescribed above following the formation of second charge transport layer5 may prevent an area having an oxygen or chlorine element density notless than two times the average density thereof in second chargetransport layer 5 from being formed adjacent to the interface betweenphotoconductive layer 4 and second charge transport layer 5. FIG. 3illustrates the composition of second charge transport layer 5 andphotoconductive layer 4 adjacent to the interface when these layers areformed in the manner as described above. Note that FIG. 3 shows thecomposition when Sb₂S₃, instead of Sb₄₅S₅₅, is used as the material ofsecond charge transport layer 5, but it is thought that the identicalresults may be obtained with respect to oxygen and chlorine elementswhen Sb₄₅S₅₅ is used. For comparison purposes, FIG. 4 shows thecomposition of second charge transport layer 5 and photoconductive layer4 adjacent to the interface thereof when second charge transport layer 5is exposed to gas that includes oxygen or water after formed and thenphotoconductive layer 4 is formed thereon. It shows that an area havingan oxygen element density not less than two times the average densitythereof in second charge transport layer 5 is formed adjacent to theinterface between second charge transport layer 5 and photoconductivelayer 4. The composition of second transport layer 5 and photoconductivelayer 4 is measured by SIMS while digging down the layers from thesecond charge transport layer side. Quantum numbers used in SIMS for S,Sb, Se, and O are 34, 121, 80, and 16 respectively.

Next, after photoconductive layer 4 is formed in the manner as describedabove, organic polymer layer 3 that includes Fullerene C₆₀ is formed. AsFullerene C₆₀, nanom purpule (C₆₀) available from Frontier CarbonCorporation is used. Polycarbonate resin (PCz) (Yupiron PCZ-400available from Mitsubishi Gas Chemical Company, Inc.) and Fullerene C₆₀are dissolved in o-dichlorobenzene at a ratio of 30 to 70 wt % toproduce a coating solution having a solid content concentration of 1.5wt %. Then, the solution is applied on photoconductive layer 4 using aninkjet coater, and the solvent is evaporated by a vacuum drier, wherebyorganic polymer layer 3 with a film thickness of 0.2 μm is obtained.

After organic polymer layer 3 is formed, the substrate is returned tothe vacuum chamber. In the present example, organic polymer layer 3 isformed by the application of solution, so that the substrate is exposedto air (gas that includes not less than 1 vol % of oxygen or water)during a period just before to after the film coating. Where organicpolymer layer 3 is formed by a method other than the coating, it ispreferable that the substrate be exposed to air before forming organicpolymer layer 3. In addition, it may also be exposed to air after that.Then, an antimony sulfide material with composition of Sb₄₂S₅₈ is heatedto a temperature of 545° C. to form first charge transport layer 2 ofantimony sulfide (with the average composition of Sb₄₂S₅₈) with a filmthickness of 0.6 μm on organic polymer layer 3, having a larger areathan organic polymer layer 3. The method for producing an antimonysulfide material having desired composition and the method for measuringthe composition of first charge transport layer 2 are identical to thoseof second charge transport layer 5.

After photoconductive layer 4 and organic polymer layer 3 are formed inthe manner as described above, formation of first charge transport layer2 after exposing the substrate to gas that includes oxygen or waterallows an area having an oxygen element density not less than threetimes the average density thereof in first charge transport layer 2 tobe provided between first charge transport layer 2 and photoconductivelayer 4. FIG. 5 illustrates the composition of first charge transportlayer 2 and photoconductive layer 4 adjacent to the interface when theselayers are formed in the manner as described above. Note that FIG. 5shows the composition when Sb₂S₃, instead of Sb₄₂S₅₈, is used as thematerial of first charge transport layer 2 and organic polymer layer 3is not provided, but it is thought that the identical results may beobtained with respect to oxygen element when Sb₄₂S₅₈ is used and organicpolymer layer 3 is provided. For comparison purposes, FIG. 6 shows thecomposition of first charge transport layer 2 and photoconductive layer4 adjacent to the interface thereof when first charge transport layer 2is formed without exposing the substrate to gas that includes oxygen orwater after photoconductive layer 4 and organic polymer layer 3 areformed. It shows that an area having an oxygen element density not lessthan three times the average density thereof in first charge transportlayer 2 is not formed adjacent to the interface between first chargetransport layer 2 and photoconductive layer 4. The composition of firsttransport layer 2 and photoconductive layer 4 is measured by SIMS whiledigging down the layers from the first charge transport layer side.Quantum numbers used in SIMS for S, Sb, Se, and O are 34, 121, 80, and16 respectively.

Finally, Au is deposited on first transport layer 2 to form biaselectrode 1 with a film thickness of 0.1 μm.

Thereafter, an evaluation of dark current, short term lag, and long termlag for Example 1 was conducted, the results of which are shown in FIG.7. In dark current measurement, charge collecting electrode 61 of activematrix substrate 6 was connected to an IV amplifier, and a currentdetected by the IV amplifier was measured with an oscilloscope whileapplying +10 KV to bias electrode 1.

In short term lag evaluation, a pulse X-ray of 710 ms was irradiated onthe Example 1 from an X-ray source with a tube voltage of 80 kV and atube current of 100 mA. The X-ray dose at the radiation image detectorwas 400 mR. Then, charge collecting electrode 61 of the active matrixsubstrate was connected to the IV amplifier, and a temporal variation ofcurrent detected by the IV amplifier was measured with an oscilloscopewhile applying +10 KV to bias electrode 1. Here, a current value after15 seconds from the termination of the pulse X-ray exposure was measuredas the evaluation value of short term lag. Preferably, the evaluationvalue of short term lag is not greater than 0.12 mR and more preferablynot greater than 0.012 mR when the current value is converted toradiation dose.

For long term lag evaluation, current flowing through charge collectingelectrode 61 was measured after the exposure of pulse X-ray, as in theshort term lag evaluation. Here, a current value after 300 seconds fromthe termination of the pulse X-ray exposure was measured as theevaluation value of long term lag. Preferably, the evaluation value oflong term lag is not greater than 0.12 mR when the current value isconverted to radiation dose.

The measurements of dark current, short term lag, and long term lag wereconducted under two conditions, emitting backlight of 20 μW/mm² ontoradiation image detector 10 from surface light source 20 and withoutemitting the backlight.

In the evaluation results shown in FIG. 7, a double circle markindicates “excellent”, a single circle mark indicates “good”, a trianglemark indicates usable, and a cross mark indicates “not usable”.

In the column of consecutive formation of second charge transport layerand photoconductive layer in the evaluation results, a single circlemark indicates that photoconductive layer 4 was formed without exposingsecond charge transport layer 5 to gas that includes oxygen or waterafter formed, and a cross mark indicates that photoconductive layer 4was formed after exposing second charge transport layer 5 to gas thatincludes oxygen or water after formed.

Further, in the column of consecutive formation of first chargetransport layer and photoconductive layer in the evaluation results, across mark indicates that first charge transport layer 2 was formedafter exposing photoconductive layer 4 to gas that includes oxygen orwater after formed, and a single circle mark indicates that first chargetransport layer 2 was formed without exposing photoconductive layer 4after formed.

FIG. 7 also indicates compositions of first and second charge transportlayers and provision or non-provision of the organic polymer layer.

As seen from FIG. 7, Example 1 shows favorable results for all measureditems of dark current, short term lag, and long term lag in comparisonwith Comparative Example 1. Comparative Example 1 was made in a manneridentical to that of Example 1 except the following. Firstly, secondcharge transport 5 of antimony sulfide (with average composition ofSb₂S₃) with a film thickness of 2 μm is formed by heating an antimonysulfide material with the composition of Sb₂S₃ to a temperature of 555°C. Then, photoconductive layer 4 is formed after second charge transportlayer 5 is exposed to gas that includes oxygen or water after formed.Secondly, the organic polymer layer is not provided, and thirdly, firstcharge transport 2 of antimony sulfide (with average composition ofSb₂S₃) with a film thickness of 0.6 μm is formed by heating an antimonysulfide material with the composition of Sb₂S₃ to a temperature of 555°C.

The favorable results of Example 1 for dark current might be attributedto the use of a material with composition of Sb₄₅S₅₅ for second chargetransport layer 5, whereby the transmission factor for the light emittedfrom surface light source 20 is reduced and light emitted tophotoconductive layer 4 is reduced.

The favorable results of Example 1 for short term lag and long term lagmight be attributed to the following. The short term lag and long termlag occur when electric charges are trapped in an area adjacent to theinterface between photoconductive layer 4 and second charge transportlayer 5. In Example 1, second charge transport layer 5 andphotoconductive layer 4 are formed consecutively, whereby the density ofoxygen or chlorine in an area adjacent to the interface thereof isreduced and the charges trapped in the area are reduced.

Further, the short term lag also occurs when electric charges are drawninto photoconductive layer 4 from bias electrode 1. The favorableresults of Example 1 for short term lag might also be attributed to thefollowing. That is, in Example 1, first charge transport layer 2 andphotoconductive layer are not formed consecutively, whereby an areawhich includes more oxygen elements is formed which acts as an electronhole blocking layer and electric charges drawn into photoconductivelayer 4 from bias electrode 1 are reduced.

Still further, the short term lag also occurs when electric charges aretrapped by defects in the interface of photoconductive layer 4 on theside of bias electrode 1. The favorable results of Example 1 for shortterm lag might also be attributed to the provision of organic polymerlayer 3, whereby the defects in the interface of photoconductive layer 4are reduced.

In the mean time, the long term lag also occurs when electric chargesare trapped by the bulk of photoconductive layer 4. The favorableresults of Example 1 for long term lag might also be attributed to theuse of a material with composition of Sb₄₂S₅₈ for first charge transportlayer 2. That is, this improves electron transportability and electriccharges trapped by the bulk of photoconductive layer 4 are dischargedefficiently to bias electrode 1.

Example 2

Example 2 was produced in the same manner as that of Example 1 otherthan that the composition of first charge transport layer 2 was changedto Sb₅₀S₅₀.

As seen from FIG. 7, Example 2 shows favorable results for all measureditems of dark current, short term lag, and long term lag in comparisonwith Comparative Example 1. Further, identical results to those ofExample 1 are obtained even though the composition of first chargetransport layer 2 is changed to Sb₅₀S₅₀.

Example 3

Example 3 was produced in the same manner as that of Example 1 otherthan that the composition of second conductive layer was changed toSb₂S₃, first charge transport layer 2 and photoconductive layer 4 wereformed consecutively without organic polymer layer 3, and thecomposition of first charge transport layer 2 was changed to Sb₂S₃.

As seen from FIG. 7, Example 1 shows improvement in short term lag andlong term lag in comparison with Comparative Example 1.

This might be attributed to the effects of consecutive formation ofsecond charge transport layer 5 and photoconductive layer 4. However,the long term lag is not improved as much as in Example 1, since thecomposition of first charge transport layer 2 is changed to Sb₂S₃.Further, the short term lag is not improved as much as in Example 1,since first charge transport layer 2 and photoconductive layer 4 areformed consecutively without organic polymer layer 3. Still further, thedark current is not improved, since the composition of second chargetransport layer 5 is changed to Sb₂S₃.

Example 4

Example 4 was produced in the same manner as that of Example 1 otherthan that first charge transport layer 2 and photoconductive layer 4were formed consecutively without organic polymer layer 3 and thecomposition of first charge transport layer 2 was changed to Sb₂S₃.

As seen from FIG. 7, Example 4 shows improvement in short term lag andlong term lag in comparison with Comparative Example 1.

This might be attributed to the effects of consecutive formation ofsecond charge transport layer 5 and photoconductive layer 4. However,the long term lag is not improved as much as in Example 1, since thecomposition of first charge transport layer 2 is changed to Sb₂S₃.Further, the short term lag is not improved as much as in Example 1,since first charge transport layer 2 and photoconductive layer 4 areformed consecutively without organic polymer layer 3. Still further, thedark current is not improved as much as in Example 1, since first chargetransport layer 2 and photoconductive layer 4 are formed consecutively,whereby more electric charges are drawn into photoconductive layer 5from bias electrode 1 and dark current is increased, although thecomposition of second charge transport layer 5 is Sb₄₅S₅₅ as in Example1.

Example 5

Example 5 was produced in the same manner as that of Example 1 otherthan that the composition of first charge transport layer 2 was changedto Sb₂S₃.

As seen from FIG. 7, Example 5 shows favorable results for all measureditems of dark current, short term lag, and long term lag in comparisonwith Comparative Example 1. However, the long term lag is not improvedas much as in Example 1, since the composition of first charge transportlayer 2 is changed to Sb₂S₃.

Example 6

Example 6 was produced in the same manner as that of Example 1 otherthan that second charge transport layer 5 was formed in a vacuumchamber, exposed to gas that includes oxygen or water, returned to thevacuum chamber and exposed to an environmental temperature not less than100° C. for a certain period of time, and thereafter photoconductivelayer 4 was formed, instead of forming them consecutively. Morespecifically, Example 6 was produced by the following steps. That is,venting the vacuum chamber with nitrogen after forming second chargetransport layer 5 to expose second charge transport layer 5 to air,evacuating the chamber again, heating second charge transport layer 5 ata temperature of 130° C. for 3 hours, reducing the temperature of secondcharge transport layer 5, and forming photoconductive layer 4 whilemaintaining the temperature of the second charge transport layer 5 at 40to 55° C.

As seen from FIG. 7, Example 6 shows favorable results for all measureditems of dark current, short term lag, and long term lag in comparisonwith Comparative Example 1. Although second charge transport layer 5 andphotoconductive layer 4 are not formed consecutively, as do in Example1, characteristics comparable to those of Example 1 are obtained byperforming the baking process in the manner as described above.

Example 7

Example 7 was produced in the same manner as that of Example 4 otherthan that photoconductive layer 4 was exposed to gas that includes notless than 1 vol % of oxygen or water (e.g., air) after formed, and thenfirst charge transport layer 2 was formed.

As seen from FIG. 7, Example 7 shows favorable results for all measureditems of dark current, short term lag, and long term lag in comparisonwith Comparative Example 1. With respect to the dark current, Example 4does not show improvement in comparison with Comparative Example 1 sincefirst charge transport layer 2 and photoconductive layer 4 are formedconsecutively, while in Example 7, they are not formed consecutively, sothat the dark current characteristics are improved in comparison withComparative Example 1 and Example 4.

Example 8

Example 8 was produced in the same manner as that of Example 7 otherthan that the composition of first charge transport layer 2 and secondcharge transport layer 5 was changed to Sb₅₀S₅₀.

As seen from FIG. 7, Example 8 shows favorable results for all measureditems of dark current, short term lag, and long term lag in comparisonwith Comparative Example 1.

1. A radiation image detection apparatus, comprising a radiation imagedetector that includes the following stacked in the order listed below:a bias electrode to which a bias voltage is applied; a photoconductivelayer that generates electric charges by receiving a recordingelectromagnetic wave representing a radiation image; a substrate sidecharge transport layer that transports the electric charges generated inthe photoconductive layer; and an active matrix substrate havingmultiple charge collecting electrodes disposed thereon for collectingthe electric charges generated in the photoconductive layer, wherein theradiation image detector does not include an area adjacent to theinterface between the substrate side charge transport layer andphotoconductive layer having an oxygen or chlorine element density notless than two times the average density thereof in the substrate sidecharge transport layer; wherein the apparatus further comprises a lightemitting means for emitting light on the radiation image detector fromthe side of the active matrix substrate while at least the recordingelectromagnetic wave is irradiated on the radiation image detector; andwherein the substrate side charge transport layer has a transmissionfactor within a range from 0.01% to 10% for the light.